Problem: $\cos(-255^{\circ}) = \text{?}$
Explanation: To find the cosine using the unit circle, first find the angle. Drag the orange point around the circle until $-255^{\circ}$ is selected. The correct angle is selected. Remember, the cosine of an angle is represented by the $x$ coordinate of a point on the unit circle. The $x$ coordinate of the point is $-0.259$, so $\cos(-255^{\circ}) = -0.259$.